.TH std::ranges::generate 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::generate \- std::ranges::generate

.SH Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::input_or_output_iterator O, std::sentinel_for<O> S,

             std::copy_constructible F >
   requires std::invocable<F&> && std::indirectly_writable<O,         \fB(1)\fP \fI(since C++20)\fP
   std::invoke_result_t<F&>>
   constexpr O

       generate( O first, S last, F gen );
   template< class R, std::copy_constructible F >

   requires std::invocable<F&> && ranges::output_range<R,
   std::invoke_result_t<F&>>                                          \fB(2)\fP \fI(since C++20)\fP
   constexpr ranges::borrowed_iterator_t<R>

       generate( R&& r, F gen );

   1) Assigns the result of successive invocations of the function object gen to each
   element in the range [first, last).
   2) Same as \fB(1)\fP, but uses r as the range, as if using ranges::begin(r) as first and
   ranges::end(r) as last.

   The function-like entities described on this page are niebloids, that is:

     * Explicit template argument lists cannot be specified when calling any of them.
     * None of them are visible to argument-dependent lookup.
     * When any of them are found by normal unqualified lookup as the name to the left
       of the function-call operator, argument-dependent lookup is inhibited.

   In practice, they may be implemented as function objects, or with special compiler
   extensions.

.SH Parameters

   first, last - the range of elements to modify
   r           - the range of elements to modify
   gen         - the generator function object

.SH Return value

   An output iterator that compares equal to last.

.SH Complexity

   Exactly ranges::distance(first, last) invocations of gen() and assignments.

.SH Possible implementation

  struct generate_fn
  {
      template<std::input_or_output_iterator O, std::sentinel_for<O> S,
               std::copy_constructible F>
      requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>>
      constexpr O operator()(O first, S last, F gen) const
      {
          for (; first != last; *first = std::invoke(gen), ++first)
          {}
          return first;
      }

      template<class R, std::copy_constructible F>
      requires std::invocable<F&> && ranges::output_range<R, std::invoke_result_t<F&>>
      constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, F gen) const
      {
          return (*this)(ranges::begin(r), ranges::end(r), std::move(gen));
      }
  };

  inline constexpr generate_fn generate {};

.SH Example


// Run this code

 #include <algorithm>
 #include <array>
 #include <iostream>
 #include <random>
 #include <string_view>

 auto dice()
 {
     static std::uniform_int_distribution<int> distr {1, 6};
     static std::random_device device;
     static std::mt19937 engine {device()};
     return distr(engine);
 }

 void iota(auto& v, int n)
 {
     std::ranges::generate(v, [&n]() mutable { return n++; });
 }

 void print(std::string_view comment, const auto& v)
 {
     for (std::cout << comment; int i : v)
         std::cout << i << ' ';
     std::cout << '\\n';
 }

 int main()
 {
     std::array<int, 8> v;

     std::ranges::generate(v.begin(), v.end(), dice);
     print("dice: ", v);
     std::ranges::generate(v, dice);
     print("dice: ", v);

     iota(v, 1);
     print("iota: ", v);
 }

.SH Possible output:

 dice: 4 3 1 6 6 4 5 5
 dice: 4 2 5 3 6 2 6 2
 iota: 1 2 3 4 5 6 7 8

.SH See also

   ranges::generate_n      saves the result of N applications of a function
   (C++20)                 (niebloid)
   ranges::fill            assigns a range of elements a certain value
   (C++20)                 (niebloid)
   ranges::fill_n          assigns a value to a number of elements
   (C++20)                 (niebloid)
   ranges::transform       applies a function to a range of elements
   (C++20)                 (niebloid)
   ranges::generate_random fills a range with random numbers from a uniform random bit
   (C++26)                 generator
                           (niebloid)
                           assigns the results of successive function calls to every
   generate                element in a range
                           \fI(function template)\fP
